A geophysical planet definition
(PHYSorg.com Space & Earth)

In 2006, during their 26th General Assembly, the International Astronomical Union (IAU) adopted a formal definition of the term `planet`. This was done in the hopes of dispelling ambiguity over which bodies should be designated as `planets`, an issue that had plagued astronomers ever since they discovered objects beyond the orbit of Neptune that were comparable in size to Pluto.